The fundamental goal of this revised PO1 proposal is to understand how pain and itch are generated by different nociceptor and pruriceptors sensory neurons and to develop techniques that can pharmacologically silence the signals responsible, as a potential novel therapeutic strategy. The program is now entirely focused on the peripheral nervous system and on the Transient Receptor Potential (TRP) TRPV1, TRPA1 and TRPV3 channels and P2X purinergic ligand-gated ion channels, both because they are key elements in the processing of sensory signals, and even more so because they are all large pore channels allowing permeation of drug molecules into the interior of nerve cells to block excitation and transmitter release. Clifford Woolf in Project 1 will identify the function of the different subsets of TRPV1l, TRPV3, TRPA1 and P2X3 expressing primary sensory neurons in pain and itch by transiently silencing their axons after delivery of the permanently charged sodium channel blocker QX-314 through the channels. Bruce Bean in Project 2 will also explore how permeation of drugs through TRP and purinergic ligand-gated ion channels can be used to silence primary sensory neurons, but by using delivery of cationic calcium channel blockers to disrupt vesicle release in the periphery to reduce neurogenic inflammation and in the spinal cord to eliminate synaptic transmission. David Clapham's Project 3 will identify how and where TRPV3 contributes to pain and itch (in keratinocytes or sensory neurons), an important issue since TRPV3 antagonists are analgesic in preclinical models and are about to be tested clinically, and will also explore if permeation of ion channel blockers through TRPV3 can be used to modify the contribution of keratinocytes and primary sensory neurons to pain and itch. Qiufu Ma in Project 4 will use genetic techniques to silence defined primary sensory neurons to tease out their specific role in pain and itch. A primary sensory neuron sp